This invention relates to a grain sorter provided with a grain sorting board and a device for moving the grain sorting board in swinging movement, and more particularly it is concerned with improvements in or relating to the device for moving the grain sorting board in swinging movement.
This type of grain sorter comprises a grain sorting board of rectangular shape having a coarse surface mounted in inclined position such that it is inclined in one direction thereof at a certain angle of inclination with respect to the horizontal and crosswise thereof too so that it is higher at one end and at one side and lower at the other end and at the other side, and a device for moving the grain sorting board in swinging movement at an angle larger than the angle of inclination. The grain sorter of the type described is constructed such that when dissimilar grain particles, such as unhulled rice and hulled rice, are supplied in mingling condition to one end of the higher side of the grain sorting board, the particles of hulled rice flow on the higher end and the particles of unhulled rice flow on the lower end owing to differences in the coefficient of friction and specific gravity between the two dissimilar grain particles, so that the particles of hulled rice and the particles of unhulled rice can be sorted and the former are discharged through the higher level portion of a grain outlet at the lower side and the latter are discharged through a lower level portion of the grain outlet at the lower side.
When the weight of the grain particles on the grain sorting board or the weight of the grain sorting board is excessively heavy, irregular vibration might be caused to occur by inertia. Also, when the device for moving the grain sorting board in swinging movement lacks balance, irregular vibration might occur. As a result, regular vibration of the grain sorting board would be interfered with and consequently the precision with which grain sorting is effected would be greatly reduced. To obviate this defect, it is essential that the weight of the swinging portion be reduced as much as possible and the center of gravity of the grain sorting board be lowered as much as possible. These are two important factors concerned in keeping the stability of the grain sorter in operation.
To efficiently carry out a grain sorting operation of high precision, it is necessary to build into the grain sorting board swinging device a mechanism for adjusting the angle of inclination of the grain sorting board so that the angle of inclination of the grain sorting board can be adjusted depending on the flow rate of grain particles, the mixing rate of dissimilar grain particles and the type of grain particles, to enable substantially the entire surface of the grain sorting board to be covered with the grain particles at all times. In this type of grain sorter of the prior art, it has hitherto been customary that the mechanism for adjusting the angle of inclination of the grain sorting board is located below the device for moving the grain sorting board in swinging movement. When this construction is used, the center of gravity of the grain sorting board is disposed at a high level, thereby making it insufficient for the grain sorting board to meet the requirements described hereinabove for enabling the grain sorter to show a stable performance.